Oats not affected by pre-harvest glyphosate

Despite buyers’ concerns, variety and environment have more impact than glyphosate

Researchers found no adverse effect on oat yield with the glyphosate application. In fact, 
they saw a slight yield bump and significantly greater test weight.

In the spring of 2015, Grain Millers announced they wouldn’t buy oats that had been treated with pre-harvest glyphosate. Christian Willenborg was alarmed.

“I was alarmed because I really hadn’t heard of an issue. I hadn’t seen an issue,” said Willenborg, assistant professor at the University of Saskatchewan and editor-in-chief of the Canadian Journal of Plant Sciences.

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“So I kind of dug into the data and I can tell you the literature’s silent on this, folks.”

That knowledge gap inspired what Willenborg called a “look-see” experiment.

The experiment

Willenborg and Nancy Ames, cereal researcher with Agriculture and Agri-Food Canada (AAFC), presented findings from a preliminary experiment examining pre-harvest glyphosate treatments on oats.

The study was done at two locations near Saskatoon, with four replications at each site. Researchers used two cultivars, CDC Dancer and AC Pinnacle.

Researchers measured the results of three different harvest systems:

  • swath at 35 per cent seed moisture;
  • direct harvest, no glyphosate; and,
  • direct harvest with a pre-harvest glyphosate treatment. It was applied at 30 per cent seed moisture at the label rate.

Researchers then measured the effects of different harvest systems on everything from test weight to milling quality. They also worked with the Canadian Grain Commission to test glyphosate residue.

Effects on yield, kernel size

The harvest systems’ effects were consistent with both oat varieties.

The swathing system saw an 18 per cent yield drop, Willenborg said. He explained they used a plot swather, which tends to lay down a poor swath in cereals. They won’t use that swather next time, he added.

“I don’t expect your yield reductions will be as great (with swathing).”

Willenborg said there was no adverse effect on yield with the glyphosate application. In fact, they saw a slight yield bump and significantly greater test weight, he added.

Researchers also found 40 per cent fewer thin kernels in the glyphosate system relative to the swathed oats. Both direct harvest systems produced more plump kernels than the swathed oats.

Researchers did detect glyphosate residue in the oats that received a pre-harvest treatment. But it was only four parts per million, which is well below allowable levels.

Willenborg noted the Canadian Grain Commission now has a glyphosate residue test for oat samples. “And we’re going to work with them and continue to send these samples in.”

While the results are preliminary, researchers found that harvest systems do affect physical quality.

“But in no instance did we see that the pre-harvest application of glyphosate had any negative influence on physical quality, relative to a well-timed swath or direct cut,” said Willenborg.

Effects on miling quality, flake quality

Ames said that in her lab “we tried to look at those quality characteristics that we thought would matter to grain millers, to others. Will this affect our marketability eventually?”

None of the harvest systems affected nutrients such as beta-glucan and protein, Ames said. But, unsurprisingly, growing location and variety did.

“These are different varieties. We expect beta-glucan to be different. These are different locations. Protein is always affected by location. Beta-glucan is affected by location,” said Ames.

Researchers also looked at oat pasting viscosity. A lower score means the oat flour will be less desirable for puffing and extrusion, Ames said. “The glyphosate treatment is no different than the straight combining. It’s exactly the same. But the swathing is considerably lower.”

All three harvest systems produced oats with similar groat breakage metrics, Ames said. The glyphosate treatment produced oats that were slightly better for milling yield, she added. Milling quality was similar in the glyphosate treatment and the other direct harvesting system.

Ames said they’d anticipated a difference with water absorption, which is one measure of flake quality.

“We do see some differences in flake quality with respect to the varieties and location, but not with the harvest treatments,” she said. Flake colour was also the same across harvest systems.

The bottom line is that variety and environment affected quality more than pre-harvest treatments, Ames said. Using glyphosate before straight combining resulted in milling quality similar to straight combining alone, she added.

Ames said they need to do more studies to see what happens when glyphosate is applied at different moisture stages.

Future work

Willenborg said they have a much larger project planned for the future. That project will look at weed control in oats and quality. Over the next two years, researchers will again examine three harvest systems; applying glyphosate pre-harvest in a direct cut, direct cutting without glyphosate, and swathing.

Each of those harvest systems will be tested at various seed moisture contents. Researchers will measure how timing affects functional quality, particularly with glyphosate treatments.

Willenborg said they also plan to measure stand uniformity. The goal is to see whether green tillers are a factor. If there’s an issue, they’ll look at whether higher seeding rates can reduce problems, he added.

The work around these studies has been funded by the Saskatchewan Oat Development Commission, the Prairie Oat Growers Association, and the Agriculture Development Fund.

A few caveats

Both Chris Willenborg and Nancy Ames noted the study was preliminary. “I caution the interpretation, because it is done just in a single year,” said Willenborg.

It’s also important to remember that research- ers followed the label when applying glyphosate before harvest.

If farmers go off-label, “that’s a black hole,” Willenborg said. “We don’t have data on that. We’re going to work on it. But at this point, if you’re doing everything by the book, so far we don’t have any indication that suggests there would be an issue there.”

The Prairie Oat Growers Association’s website also reminds farmers to follow the label when applying glypho- sate. If it’s applied pre-harvest when kernels are green (30 per cent moisture or better), farmers risk residue in the kernels that tops the limits. Farmers can avoid this by making sure the least mature parts of the field are below

30 per cent moisture. The association also notes that some customers have their own restrictions on pre-harvest glyphosate.

Willenborg also noted that the World Health Organization has declared glyphosate a possible carcinogen. Farmers and industry need to be aware of that designation, and consumer perceptions, going forward.

And finally, Willenborg reminded farmers that each additional use of glyphosate carries risks. “Most of our quarter sections are probably seeing two applications minimum per year.”

The United States has seen a 10- to 12-fold increase in glyphosate use over the last two decades, Willenborg said. Some States have 10 to 12 glyphosate-resistant weeds. And Western Canada is now seeing glyphosate-resistant weeds as well, he noted.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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